7.1 Introduction

This chapter proposes a novel hybrid OFDM/CDMA/SFH scheme [1-7]. Section 7.2 first presents a survey of existing modulation schemes providing multiple-access capability. After discussing the advantages and disadvantages of these schemes along with frequency-time diagrams, it introduces the proposed hybrid OFDM/ CDMA/SFH scheme.

Thereafter, for the sake of continuity and to familiarize the reader with direct-sequence code division multiple access (DS-CDMA) systems, the IS-95 system is discussed. The various FH schemes and their advantages and disadvantages are examined. Finally, the proposed hybrid schemes is reviewed and how it corrects the disadvantages of the earlier discussed schemes is demonstrated.

Section 7.3 compares the hybrid system to the well-known MC-CDMA system. It makes a fine distinction proposed by Yee and Linnartz [8] and then traces its evolution to the OFDM-CDMA scheme as proposed by Fazel and Papke [9]. It then discusses the MC-CDMA system and derives a mathematical expression for its operation. A similar mathematical expression is derived for the proposed hybrid system, and they are shown to be mathematically similar. However, in real terms there is a lot of difference between the two techniques. This section concludes with a detailed comparison of both the techniques, giving their advantages and disadvantages. Finally, a qualitative comparison is made in terms of the computational power required for the two systems.

Section 7.4 studies DS-CDMA, DS-slow frequency hopping (SFH), and OFDM-CDMA-SFH (hybrid) systems analytically. Initially, it compares DS-CDMA and DS-SFH. In order to make a fair comparison, it uses noncoherent modulation [differential phase...